But many Republicans brushed past this echo of Watergate and another Republican president, Richard Nixon, to maintain that no special investigation was warranted and the existing Republican-led committees will handle the probe, mostly in private.

After Flynn stepped down late Monday following reports he misled Vice President Mike Pence about contacts with a Russian diplomat, Democrats demanded the formation of an independent, bipartisan panel to examine possible links between the Trump administration and Russia, including when the president learned Flynn had discussed U.S. sanctions with a Russian diplomat.

This latest push builds on an earlier call by Democrats for an independent inquiry into Moscow's meddling in the 2016 election to help Trump beat Democrat Hillary Clinton.

"The American people deserve to know the full extent of Russia's financial, personal and political grip on President Trump and what that means for our national security," House Democratic Leader Nancy Pelosi said in a statement.

At issue is whether Flynn broke diplomatic protocol and potentially the law by discussing U.S. sanctions with Russia's ambassador to the U.S., Sergey Kislyak, before Trump's inauguration. The sanctions were imposed in December by former President Barack Obama after U.S. intelligence reported that Russia had interfered in the presidential election.

"Who knew about this and when? Did the president know and when did he know it? Did others at Trump transition team authorize conversations about sanctions?" asked Rep. Steny Hoyer, D-Md., the No. 2 House Democrat. "After the White House was informed, who made the decision to allow Flynn to continue to serve despite the fact he misled the administration?"

Sen. Claire McCaskill of Missouri, the top Democrat on the Homeland Security and Governmental Affairs Committee, said the Trump administration ought to want a "public airing" of Flynn's actions and the Russian government's attempts to influence the American political system.

"The questions are so numerous and it's really hard to get past them and begin to look infrastructure or tax reform or even confirming a Supreme Court nominee," McCaskill said.

House Speaker Paul Ryan said Flynn made the right decision to step down. But Ryan sidestepped questions about whether an inquiry is warranted.

"I'm not going to prejudge any of the circumstances surrounding this until we have all of the information," the Wisconsin Republican said.

Rep. Jason Chaffetz of Utah, the Republican chairman of the Oversight and Government Reform Committee, said "the situation has taken care of itself" when asked by reporters if his panel would investigate Flynn's actions.

"Sounds like he did the right thing, he didn't want to be a distraction," Chaffetz said of Flynn. "And it was getting to be a distraction."

Senate Intelligence committee chairman Richard Burr, R-N.C., said his panel plans "to continue to do aggressive oversight on the committee privately. We don't do that in public."

But Sen. Bob Corker of Tennessee, the Republican chairman of Foreign Relations Committee, said Congress needs to do "whatever it takes" to resolve questions about "Russia's relationship" to the 2016 presidential election.

"This is going to go on forever if we don't address it," Corker said.

Sen. Lindsey Graham, R-S.C., said he wants to know if Flynn initiated the conversations with Kislyak or if he was directed to make contact with the ambassador. He said Republicans would be "pretty upset" if after being elected former President Barack Obama had reached out to Iran or Iraq to change Bush administration policies.

"The one-president-at-a-time policy I think has served the country well," Graham said. "The idea that (Flynn) did this on his own without any direction is a good question to ask."

Republican Sen. John McCain, chairman of the Senate Armed Services Committee, said Flynn's resignation "is a troubling indication of the dysfunction of the current national security apparatus."

"General Flynn's resignation also raises further questions about the Trump administration's intentions toward Vladimir Putin's Russia, including statements by the president suggesting moral equivalence between the United States and Russia despite its invasion of Ukraine, annexation of Crimea, threats to our NATO allies, and attempted interference in American elections," McCain said in a statement.

Rep. Adam Smith, the top Democrat on the House Armed Services Committee, said revelations about Flynn's interactions with Russia "raise grave questions about who in the White House knew about Flynn's vulnerability to blackmail and exploitation by the Russian government, and when they knew about it."

Smith called for a "full investigation that covers any and all connections to these events that could undermine the national security of the United States."